Acoustic signal transmission couplants and coupling mediums

ABSTRACT

Devices, systems, and methods are disclosed for use in tomographic ultrasound imaging, large aperture ultrasound imaging and therapeutic ultrasound that provide for coupling acoustic signal transducers to body structures for transmitting and receiving acoustic signals. The acoustic signal transmission couplants can conform to the receiving medium (e.g., skin) of the subject such that there is an acoustic impedance matching between the receiving medium and the transducer. In one aspect, an acoustic coupling medium includes a hydrogel including polymerizable material that form a network structured to entrap an aqueous fluid inside the hydrogel. The hydrogel is structured to conform to the receiving body, and the acoustic coupling medium is operable to conduct acoustic signals between acoustic signal transducer elements and a receiving medium when the hydrogel is in contact with the receiving body such that there is an acoustic impedance matching between the receiving medium and the acoustic signal transducer elements.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent document is a continuation of and claims priority to U.S.patent application Ser. No. 15/053,502, filed on Feb. 25, 2016, whichclaims the benefit of priority of U.S. Provisional Patent ApplicationNo. 62/120,839, filed on Feb. 25, 2015, and U.S. Provisional PatentApplication No. 62/174,999, filed on Jun. 12, 2015. The entire contentsof the before-mentioned patent applications are incorporated byreference as part of the disclosure of this document.

TECHNICAL FIELD

This patent document relates to systems, devices, and processes foracoustic energy diagnostics and therapies.

BACKGROUND

Acoustic imaging is an imaging modality that employs the properties ofsound waves traveling through a medium to render a visual image. Highfrequency acoustic imaging has been used as an imaging modality fordecades in a variety of biomedical fields to view internal structuresand functions of animals and humans. High frequency acoustic waves usedin biomedical imaging may operate in different frequencies, e.g.,between 1 and 20 MHz, or even higher frequencies, and are often termedultrasound waves. Some factors, including inadequate spatial resolutionand tissue differentiation, can lead to less than desirable imagequality using conventional techniques of ultrasound imaging, which canlimit its use for many clinical indications or applications.

SUMMARY

Techniques, systems, and devices are disclosed for coupling acousticsignal transducers to body structures for transmitting and receivingacoustic signals in ultrasound imaging, range-Doppler measurements, andtherapies.

In one aspect, a couplant device of the disclosed technology fortransmission of acoustic energy between transducers and a targetincludes a housing body structured to present an array of transducerelements on a curved section (e.g., curved lip) of the housing body(e.g., such as a semicircular or a circular portion that exposes thetransducer elements of the array on a curved surface); and an acousticcoupling component including a hydrogel material (e.g., which may be atleast partially contained in an outer lining). The acoustic couplingcomponent is operable to conduct acoustic signals between a transducerelement disposed in the housing body and a receiving medium (e.g., skinof a subject) in contact with the acoustic coupling component topropagate the acoustic signal toward a target volume, such that theacoustic coupling component is capable to conform to the target volumesuch that there is an acoustic impedance matching (e.g., very lowattenuation) between the receiving medium and the transducer element.

The subject matter described in this patent document and attachedappendices can be implemented in specific ways that provide one or moreof the following features. For example, the couplant device can furtherinclude a flexible bracket coupled to and capable of moving with respectto the housing body, in which the flexible bracket secures the acousticcoupling component to the device. For example, the target volumeincludes a biological structure of a subject (e.g., an organ or tissue),and the receiving medium includes skin of the subject. Inimplementations of the couplant device, for example, the receivingmedium can include hair on the exterior of the skin.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a schematic diagram of an exemplary acoustic couplantdevice of the disclosed technology.

FIG. 1B shows a three dimensional view of an acoustic couplant device ofthe disclosed technology.

FIG. 1C shows another three dimensional view of an acoustic couplantdevice of the disclosed technology.

FIG. 2A shows a schematic diagram of an exemplary acoustic coupler ofthe disclosed technology attached to an exemplary flexible bracket tointerface to an array of transducing elements.

FIG. 2B shows a three dimensional view schematic diagram of an acousticcoupler attached to a flexible bracket in accordance with an exemplaryembodiment.

FIG. 2C shows a two dimensional side view schematic diagram of anacoustic coupler attached to a flexible bracket in accordance with anexemplary embodiment.

FIG. 2D shows a cross-sectional view schematic diagram of an acousticcoupler interfaced with a transducer element in accordance with anexemplary embodiment.

FIG. 3A shows a top view schematic diagram of an acoustic couplantdevice of the disclosed technology to provide a complete circular ringarray of transducer elements.

FIG. 3B shows a three dimensional schematic diagram of an acousticcouplant device of the disclosed technology to provide a completecircular ring array of transducer elements.

FIG. 4 shows a block diagram of an exemplary acoustic imaging and/ortherapy system of the disclosed technology.

FIG. 5A shows an exemplary embodiment of an acoustic coupling medium.

FIG. 5B shows another exemplary embodiment of an acoustic couplingmedium.

FIG. 5C shows another exemplary embodiment of an acoustic couplingmedium.

FIG. 5D shows another exemplary embodiment of an acoustic couplingmedium.

FIG. 5E shows another exemplary embodiment of an acoustic couplingmedium.

FIG. 5F shows another exemplary embodiment of an acoustic couplingmedium.

FIG. 5G shows another exemplary embodiment of an acoustic couplingmedium.

FIG. 6 shows schematic diagrams of an exemplary acoustic coupling mediumformed in various shapes, sizes, and configurations.

FIG. 7A shows schematic diagram of an exemplary embodiment of theacoustic coupling medium with an attachment component.

FIG. 7B shows front and side schematic views of an exemplary embodimentof the acoustic coupling medium with an attachment component.

FIG. 7C shows different schematic views of an exemplary embodiment ofthe acoustic coupling medium with a tubular curved shape.

FIG. 8 illustrates a set of operations that can be carried out toproduce acoustic waveforms using an acoustic impedance matched couplantin accordance with an exemplary embodiment.

DETAILED DESCRIPTION

Acoustic imaging can be performed by emitting an acoustic waveform(e.g., pulse) within a physical elastic medium, such as a biologicalmedium, including tissue. The acoustic waveform is transmitted from atransducer element (e.g., of an array of transducer elements) toward atarget volume of interest (VOI). Propagation of the acoustic waveform inthe medium toward the target volume can encounter structures that causethe acoustic waveform to become partly reflected from a boundary betweentwo mediums (e.g., differing biological tissue structures) and partiallytransmitted. The reflection of the transmitted acoustic waveform candepend on the acoustic impedance difference between the two mediums(e.g., at the interface between two different biological tissue types).For example, some of the acoustic energy of the transmitted acousticwaveform can be scattered back to the transducer at the interface to bereceived, and processed to extract information, while the remainder maytravel on and to the next medium. In some instances, scattering of thereflection may occur as the result of two or more impedances containedin the reflective medium acting as a scattering center. Additionally,for example, the acoustic energy can be refracted, diffracted, delayed,and/or attenuated based on the properties of the medium and/or thenature of the acoustic wave.

Acoustic wave speed and acoustic impedance differences can exist at theinterface between the transducer and the medium to receive the acousticwaveform, e.g., referred to as the receiving medium, for propagation ofthe acoustic waveform toward the target volume, which can disrupt thetransmission of the acoustic signal for imaging, range-Dopplermeasurement, or therapeutic applications. Acoustic impedance differencescaused due to differing material properties (e.g., material density) ofthe two mediums and the acoustic wave velocity, such that a substantialamount of the emitted acoustic energy will be reflected at the interfacerather than transferred in full across the interface. In typicalacoustic (e.g., ultrasound) imaging or therapy applications, forexample, a transmission gel is applied to the receiving medium (i.e.,the skin of a subject) at the interface where the transducers will makecontact to improve the transfer of the acoustic waveform(s) from thetransducer to the body and the reception of the returned acousticwaveform(s) from the body back to the transducer. In such applicationswithout the ultrasound gel, the interface may include air as a componentof the medium between the receiving medium (e.g., living skin tissue)and the transducer, and an acoustic impedance mismatch in thetransducer-to-air and the air-to-body discontinuity causes thescattering (e.g., reflection) of the emitted acoustic energy.

Despite relatively good success in reducing acoustic impedancedifference at the interface, when applied, acoustic transmission gelsmay contain tiny packets of air that can disrupt the transmission ofacoustic signals. Additionally, many patients complain of discomfortswith the use of gels applied to their skin, e.g., such as temperature,stickiness, or other. More concerning, however, acoustic transmissiongels can become contaminated during production or storage, which has ledto infections within some patients. For subjects with hair on their skinat the location where the transducer is to be placed, these subjectstypically must shave or otherwise remove the external hair whichexasperates the trapping of air between the skin and gel.

For non-normal angles of incidence of the acoustic wave relative to theinterface, the differences in the acoustic wave speed can result inrefraction of the acoustic sound wave. Acoustic wave speed differencesat the interface cause the propagation path of longitudinal acousticwaves to refract or change direction according to Snell's Law as afunction of the angle of incidence and the acoustic wave speeds eitherside of the interface. Accumulations of infinitesimal amounts ofrefraction as the wave propagates in a heterogeneous material results inbending or curvature in the path of the acoustic wave.

As conventional ultrasound imaging assumes that acoustic waves travel instraight lines, refraction along the acoustic path causes degradationand distortion in the resulting image due the ambiguity it creates forthe arrival time and location of an acoustic waveform in space for bothtransmission and reception. A material that matches the acoustic wavespeed at the interface significantly reduces the effects of refraction,resulting in a clearer and less ambiguous image. Additionally, amaterial that has a homogeneous acoustic wave speed throughout willminimize the potential for curvature of acoustic wave paths inside thematerial.

Disclosed are techniques, systems, and devices for coupling acousticsignal transducers to body structures for transmitting and receivingacoustic signals in ultrasound imaging, range-Doppler measurements, andtherapies. The disclosed acoustic signal transmission couplants canconform to the receiving medium (e.g., skin) of the subject such thatthere is an acoustic impedance matching between the receiving medium andthe transducer.

Disclosed are also various embodiments of an acoustic coupling mediumincluding a hydrogel formed from one or more polymerizable materials andcapable of conforming or molding into specific three dimensional shapesfor use in tomographic ultrasound imaging, large aperture ultrasoundimaging, and therapeutic ultrasound.

In one embodiment, a couplant device of the disclosed technology fortransmission of acoustic energy between transducers and a targetincludes a housing body including a curved surface on which an array oftransducer elements may be disposed; and an acoustic coupling componentincluding a hydrogel material, in which the acoustic coupling componentis operable to conduct acoustic signals between a transducer elementdisposed in the housing body and a receiving medium (e.g., skin of asubject) in contact with the acoustic coupling component to propagatethe acoustic signal toward a target volume, such that the acousticcoupling component is capable to conform to the receiving medium suchthat there is an acoustic impedance matching between the receivingmedium and the transducer element. In some embodiments, the couplantdevice can further include a flexible bracket coupled to and capable ofmoving with respect to the housing body, in which the flexible bracketsecures the acoustic coupling component to the device. For example, thetarget volume includes a biological structure of a subject (e.g., anorgan or tissue), and the receiving medium includes skin of the subject.In implementations of the couplant device, for example, the receivingmedium can include hair on the exterior of the skin.

FIG. 1A shows a two dimensional side view schematic diagram and FIGS. 1Band 1C show three dimensional views of an acoustic couplant device 100of the disclosed technology. The couplant device 100 includes a housingstructure 101 to contain and position transducers for transmitting andreceiving acoustic signals to/from a mass to which the acoustic couplantdevice 100 is applied. The housing structure 101 includes a curvedsection where transducer elements 110 of an acoustic transmit and/orreceive transducer array are positioned, e.g., which is shown in FIG.1C. The curved section of the housing structure 101 can be configured tovarious sizes and/or curvatures tailored to a particular body region orpart where the couplant device 100 is to be applied in acoustic imaging,measurement, and/or therapy implementations. For example, the length,depth, and arc of the curved section of the housing structure 101 can beconfigured to make complete contact with a region of interest on ananatomical structure, e.g., such as a breast, arm, leg, neck, throat,knee joint, hip joint, ankle, waist, shoulder, or other anatomicalstructure of a human or animal (e.g., canine) subject to image or applyultrasonic treatment to target volumes within such structures, such assplenic masses, cancerous or noncancerous tumors, legions, sprains,tears, bone outlines and other signs of damage or maladies. For example,the curved section of the housing structure 101 can include an aperturelength in a range of a few centimeters to tens or hundreds ofcentimeters (e.g., such as an 18 cm baseline as depicted in FIG. 1A), anaperture depth in a range of a few centimeters to tens or hundreds ofcentimeters, and an arc or curvature of 1/(half or a few centimeters) to1/(tens or hundreds of centimeters), e.g., 1/0.5 cm⁻¹ to 1/18 cm⁻¹. Thecouplant device 100 includes an acoustic coupler 105 attached to thehousing structure 101 such that the acoustic coupler 105 is in contactwith the external surface area of the transducer elements 110 disposedin the housing structure 101.

For example, the acoustic coupler 105 can be attached to the housingstructure 101 by molding the hydrogel material against the curvedsection of the housing structure 101 to directly couple the acousticcoupler 105 and the transducer elements 110 at an interface. In suchimplementations, the housing structure 101 can include a securementmechanism (e.g., such as a clip) at various locations at the curvedsection to secure the molded acoustic coupler 105 to the housingstructure 101, in which the securement mechanism is located on thehousing structure 101 at locations away from the transducer elements 110to not interfere with acoustic signal propagation transmitted andreceived by the transducer elements. In addition, or alternatively, forexample, the housing structure 101 and/or the acoustic coupler 105 caninclude an adhesive portion to attach the molded acoustic coupler 105 tothe curved section of the housing structure 101. In someimplementations, for example, the adhesive portion can be configured asan adhesive layer attached to the receiving surface of the curvedsection of the housing structure 101 and/or an outer portion of theacoustic coupler 105. In some implementations, for example, the adhesiveportion can include pretreatment of the outer portion areas of thehydrogel material of the acoustic coupler 105 (e.g., such as applying alow pH solution) to cause such areas to become naturally adhesive.

In some implementations, the acoustic coupler 105 includes a hydrogelmaterial engineered to conduct acoustic signals between transducerelements 110 and a receiving medium (e.g., body region or part of thesubject, e.g., such as the subject's midsection, head, or appendage)where the couplant device 100 is to be placed in contact to transmit andreceive the acoustic signals propagating toward and from a target volumeof interest in the subject. The acoustic coupler 105 is able to conformto the receiving medium to provide acoustic impedance matching betweenthe transducer elements and the receiving medium (e.g., the skin of thesubject, including body hair protruded from the skin).

The hydrogel material can be configured to have a selected thicknessbased on the size of the receiving body of the subject or object of theacoustic imaging, measurement, or therapy application. The diagram ofFIG. 1A depicts the acoustic coupler 105 having various thicknesses L1,L2, L3, and L4 with respect to dimensions of the curved section of thehousing structure 101. For example, in some embodiments, the L1thickness can be 4 cm, the L2 thickness can be 6 cm, the L3 thicknesscan be 8 cm, and the L4 thickness can be 10 cm, e.g., in which thecurved section of the housing structure 101 includes a semicirculargeometry with a 12 cm radius. In some implementations, for example, thehydrogel material of the acoustic coupler 105 can include polyvinylalcohol (PVA). In some implementations, for example, the hydrogelmaterial can include polyacrylamide (PAA), which can include alginate.In some embodiments, for example, the acoustic coupler 105 can includean outer lining to encase at least some portions of the hydrogel. Theexemplary outer lining can be formed over regions of the hydrogel thatare in contact with the housing structure 101. In some implementations,for example, the exemplary outer lining can be configured to fullyencase the hydrogel material to produce a pad. The hydrogel can flex,stretch and conform to any complex geometry surface to enable very lowloss and a highly matched impedance path for efficient transmission ofacoustic waveforms (e.g., ultrasonic waves) into tissue of the subject,e.g., including a human or any other animal. For example, the hydrogelcan include a material structure that allows acoustic signal propagationwith an attenuation factor of 0.1 dB/MHz²·cm or less, an impedance of1.5 MRayls or less, and a longitudinal speed of sound of 1540 m/s at 20°C. The acoustic coupler 105 is engineered to have a % elongation of1000% or greater, a density of 1.00 g/cm³±0.05 g/cm³, a shear modulus of1 MPa, and melting and freezing point of 70° C. and −5° C.,respectively. For example, the hydrogel material can be at least 95%water and have a pH of ˜7.0.

In some embodiments of the acoustic coupler 105, for example, one sideof the hydrogel and/or outer lining is configured to have a tackysurface to contact the transducer elements 110 to promote adherence tothe transducer face such that air or other substances are prohibitedfrom becoming entrapped once the couplant device 100 is applied.

In some embodiments of the couplant device 100, for example, the housingstructure 101 includes a flexible bracket 102 that attaches to thecurved section of the housing structure 101 body. In someimplementations, for example, the acoustic coupler 105 can be moldedinto the flexible bracket 102, which can also include the acousticcoupler 105 being adhesively attached (e.g., glued) to the flexiblebracket 102 at portions of the acoustic coupler 105 away from acousticsignal propagation with the transducer elements. The flexible bracket102 is structured to flex such that it can conform to the receiving bodythat it surrounds. For example, the flexible bracket 102 can includeflexible materials, e.g., including, but not limited to, ABS plastic,polyurethane, nylon, and/or acetyl copolymer. FIGS. 2A-2D showsschematic diagrams of the acoustic coupler 105 attached to the flexiblebracket 102.

FIG. 2A shows a three dimensional view schematic diagram of the acousticcoupler 105 attached to the flexible bracket 102. The flexible bracket102 can be structured to include a base component 112 to attach to theends of the acoustic coupler 105. For example, base component 112 caninclude clips to secure and/or adhere the acoustic coupler 105. In someembodiments, for example, the flexible bracket 102 can include one ormore arch components 113 configured to a size and curvature to spanacross the curved section of the housing structure 101 and positioned atone or more respective locations on the base component 112 away fromwhere the transducer elements 110 are positioned when the flexiblebracket 102 is attached to the housing structure 101. The flexiblebracket 102 can be structured to have pattern of notches 114 on one sideof the arch component(s) 113 to allow the flexible bracket 102 to bendeasily without breaking. On the other side of the arch component(s) 113,the flexible bracket 102 can include an undercut lip with a chamfer sothat when it's flexed into the shape of the array and pressed intoposition, the chamfered lip flexes over the lip on the curved section ofthe housing structure 101 and secures the flexible bracket 102, andthereby the acoustic coupler 105, in place. For example, the acousticcoupler 105 can be bonded or molded into the flexible bracket 102 whencross-linking of the hydrogel occurs. In some implementations, forexample, the hydrogel of the acoustic coupler 105 can also be molded onthe subject-facing side to smooth or curve the edges, e.g., which canallow the device 100 to contact and release from the subject easier.FIG. 2B shows a three dimensional view schematic diagram of the acousticcoupler 105 attached to the flexible bracket 102, and FIG. 2C shows atwo dimensional side view schematic diagram of the acoustic coupler 105attached to the flexible bracket 102.

FIG. 2D shows a cross-sectional view schematic diagram of the acousticcoupler 105 interfaced with a transducer element 110 and attached to thehousing structure 101 via the flexible bracket 102. As shown in thisdiagram, the acoustic coupler 105 conforms directly onto the face of thetransducer element 110. In this example, the acoustic coupler 105 isattached to the clip components of the flexible bracket 102 by anadhesive on the external surface of the clips, e.g., to align in contactwith the ‘tacky regions’ of the hydrogel and/or outer lining of theacoustic coupler 105. The clips attaches around the lip of the housingbody 101 to provide direct contact between the acoustic coupler 105 andthe face of the transducer element 110. As shown in the diagram, thetransducer element 110 includes a transducer acoustic backing portionthat interfaces with electrical communication elements for transductionof electrical to/from acoustic energy.

In some implementations of the couplant device 100, for example, thesurface of the acoustic coupler 105 in contact with the subject can belubricated so it can slide over the skin easily without trapping airbubbles for optimum acoustic transmission. Examples of such lubricantscan include treating the side of the hydrogel material that is to be incontact with the subject with degassed and/or deionized water to renderthat portion of the hydrogel material highly lubricated.

Referring back to FIGS. 1A-1C, the housing structure 101 can include oneor more handles to provide a place for a user to hold the couplantdevice 100 and/or move the couplant device 100 for positioning on thereceiving body (e.g., a subject's torso, head, appendage, etc.) for anacoustic measurement or therapy. The housing structure 101 can includeopenings at various locations on the exterior of the housing structure101 that provide access to the interior (e.g., including interiorcompartments) where electronic components including the transducerelements of the transducer array are located within the housingstructure 101. For example, as depicted in FIG. 1A, an electrical cableor wires can be electrically connected to the electronics containedwithin the housing structure 101 for data communication and/or powersupply. For example, the housing structure 101 can include compartmentsto secure signal conditioning and/or multiplexing circuitry incommunication with the transducer elements 110, e.g., L0 transducerelectronics, L1 A transducer electronics and multiplexing circuitry(e.g., multiplexing board type A), L1 B transducer electronics andmultiplexing circuitry (e.g., multiplexing board type B), and/or L2transducer level 2 MUX rigid flexible circuit card and flex mezzanineboard.

In some implementations, for example, the couplant device 110 includes amultiplexing unit contained in an interior compartment of the housingstructure 101 and in communication with the transducer elements 110 toselect one or more transducing elements 110 of the array to transmitindividual acoustic waveforms, and to select one or more transducingelements 110 of the array to receive the returned acoustic waveforms. Insome implementations of the couplant device, for example, the device 100includes a data processing unit contained in a compartment in thehousing structure 101 that includes signal conditioning circuitry toamplify the electrical signals transduced from the returned acousticsignals, and/or electrical signals to be transduced to the transmittedacoustic signals. In some embodiments of the exemplary data processingunit, for example, the data processing unit can include a processor anda memory to process and store data, respectively, which can be incommunication with an input/output (I/O) unit to interface to transmitand receive data from an acoustic imaging and/or therapy system forcontrolling operations of the data processing unit of the device 100. Insome implementations, for example, the data processing unit is incommunication with the exemplary multiplexing unit.

As depicted in FIG. 1C, which shows the flexible bracket 102 attached tothe transducer housing structure 101 without the acoustic coupler 105presently attached, the transducer elements 110 can be arranged in asemicircular configuration to span along at least part of the curvedsection of the housing structure 101. The array of transducing elements110 are presented on the curved geometry of this section of the housingstructure 101 to be in direct contact with the acoustic coupler 105 totransmit and receive acoustic signals. In the exemplary embodimentshown, the transducer elements 110 are disposed on a lip of the curvedsection of the housing structure 101. Based on the flexibility,stretchability, and conformability of the acoustic coupler 105, theacoustic coupler 105 can remain in contact with the transducer elements110 during application of the couplant device 100 as it is positionedand moved along the body structure of the subject. For example, thetransducer elements 110 are arranged on the curved section (e.g., suchas a semicircular ring, or a complete circular ring) of the housingstructure 101. The flexible bracket 102 can include clips to attach tothe lip 111 of the curved section. In some implementations, for example,the flexible bracket 102 can also include clips to secure the acousticcoupler 105 to the flexible bracket 102, which provides direct contactof the acoustic coupler 105 on to the face of the transducer elements110 on the housing structure 101.

FIGS. 3A and 3B show a top view schematic diagram and three dimensionalschematic diagram, respectively, of an acoustic couplant device 300 ofthe disclosed technology to provide a complete circular ring array oftransducer elements 110. The couplant device 300 includes a housingstructure 301 having a circular section to contain and position thetransducer elements 110 for transmitting and receiving acoustic signalsto/from a mass to which the acoustic couplant device 300 is applied. Forexample, the circular section of the housing structure 301 can include acircle geometry, elliptical geometry, or other curved geometry. Thecircular section of the housing structure 301 can be configured tovarious sizes and/or curvatures tailored to a particular body region orpart where the couplant device 300 is to be applied in acoustic imaging,measurement, and/or therapy implementations. For example, the length,depth, and geometry of the circular section of the housing structure 301can be configured to make complete contact, e.g., which can completelysurround or enclose, with a region of interest on an anatomicalstructure of a subject, e.g., such as a breast, of a human or animal(e.g., canine) to image or apply ultrasonic treatment to target volumeswithin the structure. The couplant device 300 includes the acousticcoupler 105 attached to the housing structure 301 such that the acousticcoupler 105 is in contact with the external surface area of thetransducer elements 110 disposed in the circular section of the housingstructure 301.

The couplant device 300 an include a flexible bracket 302 to attach tothe circular section of the housing structure 301 body to couple theacoustic coupler 105 to the transducer elements 110 housed in thehousing structure 301. In some implementations, for example, theacoustic coupler 105 can be molded into the flexible bracket 302, whichcan include the acoustic coupler 105 being adhesively attached to theflexible bracket 302 at portions of the acoustic coupler 105 away fromacoustic signal propagation with the transducer elements.

FIG. 4 shows a block diagram of an acoustic imaging system 400 incommunication with the acoustic couplant device 100 for acousticimaging, range-Doppler measurements, and/or therapeutic application ofacoustic energy of a target volume in a receiving body (e.g., anatomicalstructure of a human or non-human animal subject) to which the acousticcouplant device 100 is applied. Examples of acoustic systems, devices,and methods for acoustic imaging, range-Doppler measurements, andtherapies are described in U.S. Pat. No. 8,939,909, titled “SpreadSpectrum Coded Waveforms in Ultrasound Imaging,” and U.S. PatentApplication Publication No. 2015/0080725, titled “CoherentSpread-Spectrum Coded Waveforms in Synthetic Aperture Image Formation,”both of which are incorporated by reference in this patent document. Insome implementations, such acoustic systems can generate, transmit,receive, and process arbitrary or coded acoustic waveforms that create alarge, synthetic aperture. For example, coherent, spread-spectrum,instantaneous-wideband, coded waveforms can be produced in syntheticaperture ultrasound (SAU) applications using such acoustic systems,e.g., employing the disclosed acoustic coupling medium.

Referring to FIG. 4, the system 400 can include systems and/or devicesdescribed in the '909 patent and the '725 patent publication. The system400 can be used to produce acoustic waveforms transduced by the device100 (or the device 300) for transmission toward the target volume (andreception of returned acoustic waveforms), such that the acousticwaveforms have enhanced waveform properties that include aspread-spectrum, wide instantaneous bandwidth, coherency, pseudo-randomnoise characteristics, and frequency- and/or phase-coding. In someimplementations, the system 400 can be used to produce acousticwaveforms across an expanded effective (synthetic) aperture using thedevice 100 (or the device 300) for transmission toward the target volume(and reception of returned acoustic waveforms), in which the acousticwaveforms have enhanced waveform properties including a spread-spectrum,wide instantaneous bandwidth, coherent, pseudo-random noisecharacteristics, and coding.

EXAMPLES

The following examples are illustrative of several embodiments of thepresent technology. Other exemplary embodiments of the presenttechnology may be presented prior to the following listed examples, orafter the following listed examples.

In one example of the present technology (example 1), a couplant devicefor transmission of acoustic energy between transducers and a targetincludes an array of transducer elements to transmit acoustic signalstoward a target volume and to receive returned acoustic signals thatreturn from at least part of the target volume; a housing body includinga curved section on which the array of transducer elements are arranged;and an acoustic coupling component including a hydrogel material, theacoustic coupling component operable to conduct the acoustic signalsbetween a transducer element disposed in the housing body and areceiving medium in contact with the acoustic coupling component topropagate the acoustic signals toward the target volume, in which theacoustic coupling component is capable to conform to the receivingmedium and the transducer element such that there is an acousticimpedance matching between the receiving medium and the transducerelement.

Example 2 includes the device of example 1, in which the device furtherincludes a flexible bracket coupled to and capable of moving withrespect to the housing body, in which the acoustic coupling component isattached to the flexible bracket.

Example 3 includes the device of example 1, in which the hydrogelmaterial includes polyvinyl alcohol (PVA).

Example 4 includes the device of example 1, in which the hydrogelmaterial includes polyacrylamide (PAA).

Example 5 includes the device of example 4, in which the hydrogelmaterial includes alginate.

Example 6 includes the device of example 1, in which the acousticcoupling component includes an outer lining at least partially enclosingthe hydrogel material.

Example 7 includes the device of example 1, in which the acousticcoupling component is operable to propagate the acoustic signals with anattenuation factor of 0.1 dB/MHz2·cm or less, or with an impedance of1.5 MRayls or less.

Example 8 includes the device of example 1, in which the acousticcoupling component is capable to undergo a % elongation of 1000% orgreater, or includes a shear modulus of 1 MPa.

Example 9 includes the device of example 1, in which the target volumeincludes a biological structure of a living subject and the receivingmedium includes an anatomical structure of the living subject.

Example 10 includes the device of example 9, in which the curved sectionof the housing body includes a curvature to facilitate complete contactwith the anatomical structure, such that the acoustic coupling componentis in direct contact with skin of the anatomical structure.

Example 11 includes the device of example 10, in which the anatomicalstructure includes hair on the exterior of the skin.

Example 12 includes the device of example 9, in which the anatomicalstructure includes a breast, an arm, a leg, a neck including the throat,a knee joint, a hip joint, an ankle joint, an elbow joint, a shoulderjoint, an abdomen, or a chest, or a head.

Example 13 includes the device of example 9, in which the biologicalstructure includes a cancerous or noncancerous tumor, an internallegion, a connective tissue sprain, a tissue tear, or a bone.

Example 14 includes the device of example 9, in which the subjectincludes a human or a non-human animal.

Example 15 includes the device of example 1, in which the curved sectionof the housing body includes a semicircular geometry.

Example 16 includes the device of example 1, in which the curved sectionof the housing body includes a 360° circular geometry, and the array oftransducer elements arranged along the 360° circular section of thehousing body.

Example 17 includes the device of example 16, in which the 360° circularsection of the housing body and the acoustic coupling component providea curvature to facilitate complete contact around an anatomicalstructure of a living subject, and in which the device is operable toreceive the returned acoustic signals from the target volume such thatan acoustic imaging system in data communication with the device is ableto produce a 360° image of the target volume.

Example 18 includes the device of example 1, in which the device furtherincludes a multiplexing unit contained in an interior compartment of thehousing body and in communication with the array of transducer elementsto select one or more transducing elements of the array to transmitindividual acoustic waveforms, and to select one or more transducingelements of the array to receive the returned acoustic waveforms.

In one example of the present technology (example 19), an acousticwaveform system includes a waveform generation unit, an acoustic signaltransmission couplant, a multiplexing unit, and a controller unit. Thewaveform generation unit includes one or more waveform synthesizerscoupled to a waveform generator, in which the waveform generation unitis operable to synthesize a composite waveform that includes a pluralityof individual orthogonal coded waveforms corresponding to differentfrequency bands that are generated by the one or more waveformsynthesizers according to waveform information provided by the waveformgenerator, in which the individual orthogonal coded waveforms aremutually orthogonal to each other and correspond to different frequencybands, such that each of the individual orthogonal coded waveformsincludes a unique frequency with a corresponding phase. The acousticsignal transmission couplant includes a housing body including a curvedsection on which transducer elements are arranged; an array oftransducer elements to transmit acoustic waveforms corresponding to theindividual orthogonal coded waveforms toward a target volume and toreceive returned acoustic waveforms that return from at least part ofthe target volume; and an acoustic coupling component including ahydrogel material, the acoustic coupling component operable to conductthe acoustic waveforms between a transducer element disposed on thehousing body and a receiving medium in contact with the acousticcoupling component, in which the acoustic coupling component is capableto conform to the receiving medium and the transducer element such thatthere is an acoustic impedance matching between the receiving medium andthe transducer element. The multiplexing unit is in communication withthe array of transducer elements and operable to select one or moretransducing elements of an array to transduce the individual orthogonalcoded waveforms into the corresponding acoustic waveforms, and operableto select one or more transducing elements of the array to receive thereturned acoustic waveforms. The controller unit, which is incommunication with the waveform generation unit and the multiplexingunit, includes a processing unit to process the received returnedacoustic waveforms to produce a data set including information of atleast part of the target volume.

Example 20 includes the system of example 19, further including an arrayof analog to digital (A/D) converters to convert the received returnedacoustic waveforms received by the array of transducer elements of theacoustic signal transmission couplant from analog format to digitalformat as a received composite waveform that includes information of atleast part of the target volume.

Example 21 includes the system of example 19, further including a userinterface unit in communication with the controller unit.

Example 22 includes the system of example 19, in which the produced dataset includes an image of at least part of the target volume.

Example 23 includes the system of example 19, in which the acousticsignal transmission couplant includes a flexible bracket coupled to andcapable of moving with respect to the housing body, in which theacoustic coupling component is attached to the flexible bracket.

Example 24 includes the system of example 23, in which the hydrogelmaterial includes at least one of polyvinyl alcohol (PVA),polyacrylamide (PAA), or PAA with alginate.

Example 25 includes the system of example 19, in which the curvedsection of the housing body of the acoustic signal transmission couplantincludes a semicircular geometry, or the curved section of the housingbody of the acoustic signal transmission couplant includes a 360°circular geometry such that the array of transducer elements arearranged along the 360° circular section of the housing body.

Example 26 includes the system of example 25, in which the 360° circularsection of the housing body and the acoustic coupling component providea curvature to facilitate complete contact around an anatomicalstructure of a living subject, and in which the device is operable toreceive the returned acoustic waveforms from the target volume such thatthe system is able to produce a 360° image of the target volume.

In one example of the present technology (example 27), a method ofproducing acoustic waveforms using an acoustic impedance matchedcouplant includes: synthesizing, in one or more waveform synthesizers,one or more composite waveforms to be transmitted toward a target, inwhich a composite waveform is formed of a plurality of individualorthogonal coded waveforms that are mutually orthogonal to each otherand correspond to different frequency bands, such that each of theindividual orthogonal coded waveforms includes a unique frequency with acorresponding phase; transmitting, from one or more transmittingpositions relative to the target using an array of transducing elementsof an acoustic signal transmission couplant, one or more compositeacoustic waveforms that includes a plurality of acoustic waveforms, inwhich the transmitting includes selecting one or more of the transducingelements of the array to transduce the plurality of individualorthogonal coded waveforms of the respective one or more compositewaveforms into the plurality of corresponding acoustic waveforms of therespective one or more composite acoustic waveforms; and receiving, atone or more receiving positions relative to the target, returnedacoustic waveforms that are returned from at least part of the targetcorresponding to the transmitted acoustic waveforms, in which thereceiving includes selecting at least some of the transducing elementsof the array to receive the returned acoustic waveforms, in which thetransmitting positions and the receiving positions each include (i)spatial positions of the array of transducer elements relative to thetarget and/or (ii) beam phase center positions of the array, in whichthe acoustic signal transmission couplant includes an acoustic couplingcomponent including a hydrogel material operable to conduct the acousticwaveforms between the transducer elements and a receiving medium incontact with the acoustic coupling component, in which the acousticcoupling component is capable to conform to the receiving medium and thetransducer element such that there is an acoustic impedance matchingbetween the receiving medium and the transducer element, and in whichthe transmitted acoustic waveforms and the returned acoustic waveformsproduce an enlarged effective aperture.

Example 28 includes the method of example 27, further includingprocessing the received returned acoustic waveforms to produce an imageof at least part of the target.

As noted earlier, some of the disclosed embodiments relate to anacoustic coupling medium including a hydrogel formed from one or morepolymerizable materials and capable of conforming or molding intospecific three dimensional shapes for use in tomographic ultrasoundimaging, large aperture ultrasound imaging, and therapeutic ultrasound.

Hydrogel materials contain mostly water, thus, the acoustic wave speedof the hydrogel is dominated by water. The acoustic wave speed in wateris approximately proportional to temperature through a high orderempirically-determined polynomial relationship from 0 to 100° C. Theacoustic wave speed of pure water varies from 1482 m/s to 1524 m/s from20° C. to 37° C., respectively. Thus, the acoustic wave speed in apolymeric material will vary with temperature.

A material with a calibrated acoustic wave speed may be used incombination with a delay-and-sum beamformer to correct the propagationtimes on transmission and reception in order to reduce image distortioncreated by uncalibrated coupling materials. For example, the location ofa structure such as a tissue-bone interface is ambiguous withoutknowledge of the average acoustic wave speed between the array and thebone. The true location of the bone may be deeper or shallower than itmeasures on the ultrasound image.

A material with a temperature calibrated acoustic wave speed such thatthe material may be heated in order to provide a more comfortableinterface to the patient without creating image distortion. Besidespatient comfort, a heated material also supports increased blood flow inthe region in contact with the patient and in regions peripheral to theregion in contact, thus facilitating more accurate Doppler measurements.A material with a calibrated acoustic wave speed will also functionoptimally at a target temperature (e.g. 37° C.) or target range oftemperatures (e.g. 20-37° C.).

Thermocouples, thermistors, fiber-optic thermometers or othertemperature sensing devices may be implanted into the hydrogel toprovide real-time temperature feedback. Additionally, wires, resistors,thermopiles, electrical current, infrared radiation, water pipes,conduction, or other means to heat the hydrogel may be utilized to heatthe gel. A temperature feedback and control device may be utilized toprecisely and accurately control the temperature of the hydrogel.

The disclosed acoustic coupling medium can be employed in acousticimaging, range-Doppler measurement, and therapeutic systems to transferemitted and returned acoustic waveforms between such acoustic systemsand a receiving medium, such as tissue of a living organism.

In some implementations of the disclosed acoustic coupling technology,for example, a hydrogel acoustic coupling medium of the presenttechnology can provide spatially-varying acoustic absorption for usewith acoustic imaging, diagnostic and/or therapeutic devices or systemsto provide tomographic ultrasound imaging, large aperture ultrasoundimaging arrays, and therapeutic ultrasound arrays for such acousticdevices and systems. In some implementations of the disclosedtechnology, the hydrogel acoustic coupling medium can couple acousticwaves from acoustic energy sources into the hydrogel acoustic couplingmedium and subsequently into secondary media with acoustic sound speedsranging from 1400 m/s up to 1700 m/s. Examples of the secondary mediainclude, but are not limited to, mammalian tissues and water. Thesecondary media may contain structures with sound speeds outside thesound speed range of the coupling medium, e.g., such as bone, implanteddevices, plastics, ceramics, glass, and metals.

In practical applications of ultrasound imaging, particularly forimaging human and nonhuman animals, ultrasound image formation typicallyoccurs in the near field of an acoustic emission aperture, which posesseveral challenges for obtaining high resolution and quality ultrasoundimages. For example, in such ultrasound imaging applications, generally,one or more transducer elements are included in an acoustic imagingdevice, forming an array, to generate the acoustic aperture. Thesetransducer elements typically require several wavelengths to transitionfrom the near field to the far field regime following an acousticemission, thus requiring an acoustic buffer region, also known as anacoustic standoff. For example, this acoustic buffer region or acousticstandoff may be necessary for image formation close to the acousticaperture. Furthermore, focused image formation typically requires thatthe ratio of the focal depth divided by the aperture size (e.g., alsoknown as the f-number) be greater than one, e.g., for points of theimage formation closest to the acoustic aperture. Likewise, the acousticstandoff is necessary for image formation close to the acoustic aperturein order to satisfy the f-number condition.

In implementations of the disclosed technology, the image formation isgenerated using combinations of the transducer elements, in which aselected group of transducer elements are used to produce an acousticemission followed by reception of return acoustic echoes on some, thesame, and/or other transducer elements of the group. For example, thetransducer elements producing the acoustic emission are referred to astransmit elements. Likewise, the transducer elements that receive thereturn acoustic echoes are referred to as receive elements. In someexamples, the combinations may be divided into combinations ofindividual pairs of transmit and receive elements such that the linearcombination of the pairs produces an approximately equivalent image asobtained using the combinations of one or more elements on both transmitand receive. For example, each time sample of an echo recorded from thepair of transmit and receive elements is an integration of acousticreflectivity over the corresponding round-trip time or time delaycorresponding to the time sample. The integration is a line integralover linear paths of the constant round-trip time or time delay. Thelinear paths can be circular or elliptical as determined by the locationof the pair of transmit and receive elements. In practice, for example,the circular or elliptical paths may extend to highly reflectiveinterfaces including, but not limited to, the interface between theacoustic coupling medium and a low acoustic impedance material, e.g.,such as air or plastic, or the interface between the acoustic couplingmedium and a high acoustic impedance material, e.g., such as metal orceramic.

Acoustic reflections from the interfaces, also known as specularreflections, contaminate the line integrals of reflectivity and thecorresponding echo samples obtained from the transmit and receivecombinations. In general, for the acoustic reflections observed for thecombination of transmit and receive elements, the angle of incidencemeasured from the transmit element to a point on the reflectiveinterface to the surface normal vector for a point lying on thereflective interface equals the angle of reflection measured from thesame normal vector to the vector defined by the point on reflectiveinterface to the receive element. The acoustic reflection can havemirror or amphichiral symmetry. The acoustic reflection has power equalto the acoustic impedance of the secondary medium minus the acousticimpedance of the coupling medium, divided by the acoustic impedance ofthe secondary medium plus the acoustic impedance of the coupling medium,as described in Equation (1).

$\begin{matrix}{P_{r} = \frac{\left( {Z_{2m} - Z_{cm}} \right)}{\left( {Z_{2m} + Z_{cm}} \right)}} & (1)\end{matrix}$

The contamination caused by the acoustic reflection can preclude the useof the transmit and receive combinations in beamformers based on delayedand summed echo samples, also known as a delay-and-sum beamformer. Suchpreclusion of echo samples can result in removal of the transmit andreceive combination from the delay-and-sum beamformer, thus limiting thequality of the image pixel corresponding to the delay-and-sumbeamformer. The image pixel quality is a function of thepoint-spread-function of the limited set of transmit and receivecombinations. Such preclusion of echo samples can also reduce thesignal-to-noise ratio (SNR) for the image pixel. Additionally, for theapertures with an array pitch greater than one-half wavelength, theimage pixel locations that require transmitter and receiver combinationsto steer away from zero degrees (0°) will be increasingly subject tograting lobes with increasing steering angle and increasing array pitch.Such grating lobes add to the sensitivity and complexity of the specularreflections.

The acoustic coupling medium of the disclosed technology can beconfigured in an acoustic couplant device and operable to conductacoustic signals between a transducer element disposed in a housing bodyof the couplant device and a receiving medium (i.e., the secondarymedium, e.g., skin of a subject) in contact with the acoustic couplingmedium to propagate the acoustic signal toward a target volume. Thedisclosed acoustic coupling medium is capable to conform to the targetvolume such that there is an acoustic impedance matching (e.g., very lowreflection) between the receiving medium and the transducer element.

The disclosed acoustic coupling medium is configured to havethree-dimensional shape. In some examples of the disclosed acousticcoupling medium, for example, an acoustic coupling medium is engineeredinto a specific three-dimensional shape for a particular implementationutility, e.g., for tomographic acoustic imaging, large aperture acousticimaging, and/or therapeutic acoustic treatment. In one exampleembodiment shown in FIG. 5A, an acoustic coupling medium 505A includesshape of a tube with an inner radius, an outer radius, and a height. Thetubular acoustic coupling medium 505A includes a hydrogel including oneor more polymerizable materials and capable of conforming or moldinginto specific three dimensional shapes for desired applications. Theradii and the height of the acoustic coupling medium 505A can vary basedon each application. For example, due to the elasticity and tensilestrength of the coupling medium 505A, the tubular shape is flexible andcapable of stretching around irregularly shaped secondary media, e.g.,such as limbs of a human or nonhuman animal. As shown in FIG. 5A, theacoustic coupling medium 505A is attached to the housing body 501 of anacoustic couplant device. The acoustic coupling medium 505A isconfigured such that, when placed in contact with a subject, thecoupling medium 505A also maintains constant contact with the secondarymedia of the subject, e.g., maintaining complete contact with thesubject's skin, including around irregular structures such as elbows andknees.

Additionally, the tubular coupling medium is compatible with tomographicapertures ranging from 0 to 360 degrees around the secondary medium,e.g., subject's limbs, torso, head, etc., while maintaining acousticcontact over the entire aperture and secondary medium, simultaneously.With applied force, constant contact may be maintained with movement ofthe aperture over the coupling medium. For example, the tomographicapertures with a polygon shape, the flexible coupling medium maintainscontact over the surface of the entire aperture, including betweenfacets of the polygon. The exemplary tubular shape of the acousticcoupling medium 505A may be molded to match any three-dimensional shapeof the aperture, including polygon shapes. For example, for tomographicapertures less than 360 degrees, the exemplary tubular acoustic couplingmedium 505A does not have highly reflective air interfaces at sharpedges that would exist for coupling media extending only over theaperture. At the edges of the aperture, the transmit and receivecombinations are able to function unrestricted by the tubular couplingmedium 505A, thus obviating the need for preclusion of the combinationfrom the beamformer. The reflective air interface extending around theentire coupling medium keeps wide angle and primary reflectionsinternally reflecting around the acoustic coupling medium 505A, wherethey are attenuated and end up being incoherent acoustic noise.

FIG. 5B shows another arrangement of the exemplary tubular acousticcoupling medium 505A placed in contact with a body portion of thesubject to conform with complete contact with the secondary medium. Theexample arrangement shown in FIG. 5B provides the ability for theinternal reflections to be further broken up by one or more gaps in thetubular acoustic coupling medium 505A.

FIG. 5C shows another example embodiment of an acoustic coupling medium505C that includes the hydrogel and an acoustically attenuating regionin one or more portions of the hydrogel. For example, in acoustictransmission operations, the internal reflections may be absorbed withthe acoustically attenuating region in the tubular acoustic couplingmedium 505C.

For example, such attenuation may be obtained through absorption orscattering or both. The acoustic attenuation region can be structured toinclude one or more of higher density polymers, higher absorptionpolymers, scatterers, microbubbles, microballoons, plastics, rubbers, orother absorptive materials.

FIG. 5D shows another example embodiment of an acoustic coupling medium505D that includes the hydrogel and configured in a flattened shapeconvertibly adapted to a tubular shape. For example, the tubular shapemay be formed from a rectangular block of the acoustic coupling medium505D, which is wrapped around the secondary medium (e.g., of thesubject). The wrapped coupling medium may be trimmed using a cuttingdevice and attached end-to-end with an attachment device, e.g.,including, but not limited to, straps, velcro, buttons, zipper, latch,gripper, or some other mechanical attachment device, or a chemical bond.FIG. 5E shows an example of the shape convertible acoustic couplingmedium 505D conformed around a body portion of a subject and attached atcontactable ends by an attachment component.

In addition to a tubular shape, the acoustic coupling medium may beshaped with a partial tubular shape of less than 360 degrees in thetransverse plane, such that it can partially cover the secondary mediumof the subject, e.g., subject's limbs, torso, head, etc., and can extendup to or beyond the boundaries of the aperture, as shown in FIG. 5F.FIG. 5F shows another example embodiment of an acoustic coupling medium505F that includes the hydrogel and configured in a partial tubularshape that is less than 360 degrees conformed to a subject's bodyportion. The acoustic coupling medium is shown in FIG. 5F to be attachedto the body housing 101 of an acoustic couplant device.

In some embodiments of the acoustic coupling medium, the partial tubularacoustic coupling medium 505F may be structured to include acousticallyattenuating regions in one or more portions of the acoustic couplingmedium. As shown in FIG. 5G, an acoustic coupling medium 505G includesthe hydrogel and two acoustic attenuating regions located at ends of thepartial tube coupling shape to provide acoustically attenuatingproperties to the acoustic coupling medium 505G.

In various embodiments of the disclosed acoustic coupling medium, thehydrogel can include one or more polymerizable materials that polymerizein the presence of water into hydrophilic gels formed from a natural orsynthetic network of polymer chains. Examples of such polymerizablematerials include, but are not limited to, polymers and polymerderivatives, alginate, agarose, sodium alginate, chitosan, starch,hydroxyethyl starch, dextran, glucan, gelatin, Poly(vinyl alcohol)(PVA), Poly (N-isopropylacrylamide) (NIPAAm), Poly(vinylpyrrolidone)(PVP), Poly(ethylene glycol) (PEG), Poly(acrylic acid) (PAA), acrylatepolymers, Polyacrylamide (PAM), Poly(hydroxyethyl acrylate) (PHEA),Poly(2-propenamide), Poly(1-carbamoylethylene), and Poly(hydroxyethylmethacrylate) (PHEMA). In fabrication techniques to produce thehydrogel, the polymerizable materials can be polymerized through severalprocesses, which may involve toxic or non-toxic chemical compounds,ultraviolet light, irradiation, toxic or nontoxic solvents, temperaturecycling, and freeze-thaw cycling. In some implementations to produce thehydrogel, polymerization of the hydrogel through freeze-thaw cycling canbe performed, due to the absence of potentially toxic compounds.

For example, the hydrogel can include a material structure that allowsacoustic signal propagation with an attenuation factor of 1.0 dB/MHz/cmor less, an impedance of 2.0 MRayls or less, and a longitudinal speed ofsound of 1700 m/s or less at 20° C. The acoustic coupler 105 isengineered to have a % elongation of 100% or greater, a density rangingfrom 1.00-1.20 g/cm³, a shear modulus of less than 1 MPa, and meltingand freezing points near 70° C. and −5° C., respectively. For example,the hydrogel material can be at least 90% water and have a pH of ˜7.0.

In a some embodiments of the acoustic coupling medium, the hydrogel canprimarily include water or equivalent solvent and the polymer Poly(vinylalcohol) (PVA) through the example polymerization process of freeze-thawcycling, which is a biocompatible polymer and a biocompatiblepolymerization process for the polymer. The addition of othercomponents, e.g., such as solvents (such as ethyl alcohol or dimethylsulfoxide) and/or other polymers (such as alginate or gelatin), to thisexample PVA hydrogel may be employed, as such additional components canbe used to improve mechanical or acoustic properties. For example, theaddition of one or more bacteriostatic chemicals with sufficientconcentration and compatibility with the hydrogel integrity can maintainsterility of the hydrogel during storage and use.

Notwithstanding other mechanically, acoustically, and biologicallyequivalent formulations, the utility of a hydrogel for its acousticproperties due to its high water content, its high tensile strength, andits elasticity is an advantageous feature of the disclosed acousticcoupling medium. The sound speed and acoustic attenuation of thehydrogel may be controlled by varying polymer concentration, waterconcentration, additional solvent concentration, degree ofpolymerization, method of polymerization, and inclusion of additionalmaterials such as scattering and/or acoustically absorbing materials.

In one embodiment, for example, the hydrogel includes PVA in a weightratio of 1-10% and H₂O in a weight ratio of 90-99%. The hydrogel iscross-linked through application of 1-10 controlled freeze-thaw cyclescycling in the range of −40° C. to 70° C.

In another embodiment, for example, the hydrogel includes PVA in aweight ratio of 1-10%, DMSO in a weight ratio of 1-10%, and H₂O in aweight ratio of 80-98%. The hydrogel is cross-linked through applicationof 1-10 controlled freeze-thaw cycles cycling in the range of −40° C. to70° C.

In another embodiment, for example, the hydrogel includes PVA in aweight ratio of 4-10%, PVP in a weight ratio of 1-5%, DMSO in a weightratio of 1-10%, and H₂O in a weight ratio of 75-94%. The hydrogel iscross-linked through application of 1-10 controlled freeze-thaw cyclescycling in the range of −40° C. to 70° C.

In another embodiment, for example, the hydrogel includes PVA in aweight ratio of 4-10%, PVP in a weight ratio of 1-5%, polyethyleneglycol in a weight ratio of 1-5%, and H₂O in a weight ratio of 80-94%.The hydrogel is cross-linked through application of 1-10 controlledfreeze-thaw cycles cycling in the range of −40° C. to 70° C.

In another embodiment, for example, the hydrogel includes PVA in aweight ratio of 4-10%, PVP in a weight ratio of 1-5%, sodium tetraboratein a weight ratio of 1-5%, and H₂O in a weight ratio of 80-94%. Theborate ions react with hydroxyl groups to cross-link the polymer. Themixture is maintained at a constant temperature during cross-linking.

FIG. 6 shows three dimensional schematic diagrams of an exemplaryacoustic coupling medium 505 formed in various shapes, sizes, andconfigurations. In one example, an acoustic coupling medium 505A′ isconfigured to have a shape similar to a half cylinder with a 180°curvature, and diameter and depth designed to an initial size, and whichare variable to conform to a particular receiving body. In this example,the acoustic coupling medium 505A′ can be configured to have a volume of3.15 L, which is retained in any shape to which the acoustic couplingmedium 505A′ is conformed. In another example, an acoustic couplingmedium 105B′ is configured to have a cylindrical shape with a diameterand depth designed to an initial size, and which are variable to conformto a particular receiving body. In this example, the acoustic couplingmedium 105B′ can be configured to have a volume of 5.75 L. In otherexamples, acoustic coupling mediums 505C′, 505D′, 105E′, and 505F′ areconfigured to have a half-cylinder shape similar to a half donut with a180° curvature and initial outer diameter and depth designed to aninitial size, in which the initial inner diameter of the acousticcoupling mediums 505C′, 505D′, 105E′, and 505F′ is designed to differingsizes (e.g., 40, 80, 120, and 160 mm, respectively), and which the sizesare variable to conform to a particular receiving body, e.g., such assurround the subject's arm, leg, neck, etc. In these examples, theacoustic coupling mediums 505C′, 505D′, 105E′, and 505F′ can beconfigured to have a volume of 3.0 L, 2.75 L, 2.3 L, and 1.7 L ,respectively.

FIGS. 7A-7C show schematic diagrams of exemplary embodiments of theacoustic coupling medium 505D and 505A, featuring three dimensional,front, and side views. As shown in FIG. 7A, the acoustic coupling medium505D includes the hydrogel configured in a tubular curved shape, whichmay be wrapped around the secondary medium of the subject and secured byattachment of the attachment component on each end of the hydrogel. Theleft drawing of FIG. 7A shows a three dimensional schematic view of thehydrogel and the attachment component of the acoustic coupling medium505D presently detached, and the right drawing of FIG. 7A shows atransparent three dimensional schematic view of the hydrogel secured inthe tubular configuration by attachment of the attachment component. Inthe examples shown in FIG. 7A, the attachment component is structured toinclude a curved base portion that is sized to the initial size of thedepth of the hydrogel and having the same arc curvature as the hydrogelin the tubular configuration. The attachment component is structured toinclude one or more sets of opposing protrusion structures on the insidesurface of the base portion capable of penetrating into the hydrogel tosecure the hydrogel in the tubular shape. FIG. 7B shows a transparentfront view and a transparent side view of the acoustic coupling medium505D with the attachment component secured to the hydrogel.

FIG. 7C shows the acoustic coupling medium 505A including the hydrogelconfigured in a 360° tubular curved shape. The left drawing shows athree dimensional schematic view of the acoustic coupling medium 505A,the center drawing shows a front view of the acoustic coupling medium505A, and the right drawing shows a side view of the acoustic couplingmedium 505A. As depicted in the drawings of FIG. 7C, in this example,the acoustic coupling medium 505A includes a beveled edge at theinterface between the outer circular plane surfaces and the outer curvedsurface, as well as a beveled edge between the outer circular planesurfaces and the inner curved surface. For example, the beveled edge mayprovide easier and secure loading and unloading of the coupling medium505A in and out of a bracket or other holder of an acoustic couplantdevice.

FIG. 8 illustrates a set of operations that can be carried out toproduce acoustic waveforms using an acoustic impedance matched couplantin accordance with an exemplary embodiment. At 802, in one or morewaveform synthesizers, one or more composite waveforms are synthesizedto be transmitted toward a target. A composite waveform is formed of aplurality of individual orthogonal coded waveforms that are mutuallyorthogonal to each other and correspond to different frequency bandssuch that each of the individual orthogonal coded waveforms includes aunique frequency with a corresponding phase. At 804, one or morecomposite acoustic waveforms are transmitted, from one or moretransmitting positions relative to the target using an array oftransducing elements of an acoustic signal transmission couplant. Theone or more composite acoustic waveforms include a plurality of acousticwaveforms, and the transmitting includes selecting one or more of thetransducing elements of the array to transduce the plurality ofindividual orthogonal coded waveforms of the respective one or morecomposite waveforms into the plurality of corresponding acousticwaveforms of the respective one or more composite acoustic waveforms. At806, at one or more receiving positions relative to the target, returnedacoustic waveforms are received that are returned from at least part ofthe target corresponding to the transmitted acoustic waveforms.Reception of the returned acoustic waveforms includes selecting at leastsome of the transducing elements of the array to receive the returnedacoustic waveforms. When conducting the above operations, thetransmitting positions and the receiving positions each include (i)spatial positions of the array of transducer elements relative to thetarget and/or (ii) beam phase center positions of the array. Further,the acoustic signal transmission couplant includes an acoustic couplingcomponent including a hydrogel material operable to conduct the acousticwaveforms between the transducer elements and a receiving medium incontact with the acoustic coupling component. The acoustic couplingcomponent is capable of conforming to the receiving medium and thetransducer element such that there is an acoustic impedance matchingbetween the receiving medium and the transducer element. The transmittedacoustic waveforms and the returned acoustic waveforms produce anenlarged effective aperture.

Implementations of the subject matter and the functional operationsdescribed in this patent document can be implemented in various systems,digital electronic circuitry, or in computer software, firmware, orhardware, including the structures disclosed in this specification andtheir structural equivalents, or in combinations of one or more of them.Implementations of the subject matter described in this specificationcan be implemented as one or more computer program products, i.e., oneor more modules of computer program instructions encoded on a tangibleand non-transitory computer readable medium for execution by, or tocontrol the operation of, data processing apparatus. The computerreadable medium can be a machine-readable storage device, amachine-readable storage substrate, a memory device, a composition ofmatter effecting a machine-readable propagated signal, or a combinationof one or more of them. The term “data processing apparatus” encompassesall apparatus, devices, and machines for processing data, including byway of example a programmable processor, a computer, or multipleprocessors or computers. The apparatus can include, in addition tohardware, code that creates an execution environment for the computerprogram in question, e.g., code that constitutes processor firmware, aprotocol stack, a database management system, an operating system, or acombination of one or more of them.

A computer program (also known as a program, software, softwareapplication, script, or code) can be written in any form of programminglanguage, including compiled or interpreted languages, and it can bedeployed in any form, including as a stand-alone program or as a module,component, subroutine, or other unit suitable for use in a computingenvironment. A computer program does not necessarily correspond to afile in a file system. A program can be stored in a portion of a filethat holds other programs or data (e.g., one or more scripts stored in amarkup language document), in a single file dedicated to the program inquestion, or in multiple coordinated files (e.g., files that store oneor more modules, sub programs, or portions of code). A computer programcan be deployed to be executed on one computer or on multiple computersthat are located at one site or distributed across multiple sites andinterconnected by a communication network.

The processes and logic flows described in this specification can beperformed by one or more programmable processors executing one or morecomputer programs to perform functions by operating on input data andgenerating output. The processes and logic flows can also be performedby, and apparatus can also be implemented as, special purpose logiccircuitry, e.g., an FPGA (field programmable gate array) or an ASIC(application specific integrated circuit).

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andany one or more processors of any kind of digital computer. Generally, aprocessor will receive instructions and data from a read only memory ora random access memory or both. The essential elements of a computer area processor for performing instructions and one or more memory devicesfor storing instructions and data. Generally, a computer will alsoinclude, or be operatively coupled to receive data from or transfer datato, or both, one or more mass storage devices for storing data, e.g.,magnetic, magneto optical disks, or optical disks. However, a computerneed not have such devices. Computer readable media suitable for storingcomputer program instructions and data include all forms of nonvolatilememory, media and memory devices, including by way of examplesemiconductor memory devices, e.g., EPROM, EEPROM, and flash memorydevices. The processor and the memory can be supplemented by, orincorporated in, special purpose logic circuitry.

While this patent document contain many specifics, these should not beconstrued as limitations on the scope of any invention or of what may beclaimed, but rather as descriptions of features that may be specific toparticular embodiments of particular inventions. Certain features thatare described in this patent document in the context of separateembodiments can also be implemented in combination in a singleembodiment. Conversely, various features that are described in thecontext of a single embodiment can also be implemented in multipleembodiments separately or in any suitable subcombination. Moreover,although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. Moreover, the separation of various system components in theembodiments described in this patent document should not be understoodas requiring such separation in all embodiments.

Only a few implementations and examples are described and otherimplementations, enhancements and variations can be made based on whatis described and illustrated in this patent document.

What is claimed is:
 1. An acoustic coupling medium for acoustic signaltransmission, comprising: a semi-rigid material able to conform to botha surface of a receiving body and to an array of acoustic signaltransducer elements, such that the semi-rigid material is operable topropagate acoustic signals between the acoustic signal transducerelements and a receiving medium of the receiving body and provide anacoustic impedance matching of 2.0 MRayls or less between the receivingmedium and the acoustic signal transducer elements, wherein the acousticcoupling medium is operable to propagate the acoustic signals with anattenuation factor of 1.0 dB/MHz·cm or less.
 2. The acoustic couplingmedium of claim 1, wherein the acoustic coupling medium includes a shearmodulus of 1 MPa.
 3. The acoustic coupling medium of claim 1, whereinthe acoustic coupling medium includes a density ranging from 1.00-1.20g/cm3.
 4. The acoustic coupling medium of claim 1, wherein the acousticcoupling medium is operable to propagate the acoustic signals with alongitudinal speed of sound at 1700 m/s or less at 20° C.
 5. Theacoustic coupling medium of claim 1, wherein the acoustic couplingmedium is capable to undergo a percent elongation of 100% or greater. 6.The acoustic coupling medium of claim 1, wherein the semi-rigid materialincludes one or more polymerizable materials that form a networkstructured to entrap an aqueous fluid inside.
 7. The acoustic couplingmedium of claim 6, wherein the one or more polymerizable materialsinclude one or more of alginate, agarose, sodium alginate, chitosan,starch, hydroxyethyl starch, dextran, glucan, gelatin, Poly(vinylalcohol) (PVA), Poly (N-isopropylacrylamide) (NIPAAm),Poly(vinylpyrrolidone) (PVP), Poly(ethylene glycol) (PEG), Poly(acrylicacid) (PAA), acrylate polymers, Polyacrylamide (PAM), Poly(hydroxyethylacrylate) (PHEA), Poly(2-propenamide), Poly(l-carbamoylethylene), orPoly(hydroxyethyl methacrylate) (PHEMA).
 8. The acoustic coupling mediumof claim 6, wherein the aqueous fluid includes water.
 9. The acousticcoupling medium of claim 8, wherein the water is at least 90% weight ofthe semi-rigid material.
 10. The acoustic coupling medium of claim 6,wherein the semi-rigid material is able to conform to the surface of thereceiving body in complete contact to the surface without packets of airor voids formed between the acoustic coupling medium and the receivingbody.
 11. The acoustic coupling medium of claim 1, further comprising anouter lining at least partially enclosing the semi-rigid material. 12.The acoustic coupling medium of claim 1, wherein the semi-rigid materialis structured to have a tubular cylindrical shape including a hollowinterior having a 360° curvature formed between opposing openings on endsurfaces of the tubular cylindrical shape, or wherein the semi-rigidmaterial is structured to have a half tubular cylindrical shapeincluding a curved inner surface and a curved outer surface each havinga 180° curvature between opposing ends of the tubular cylindrical shape.13. The acoustic coupling medium of claim 1, wherein the semi-rigidmaterial includes an acoustic attenuation region to scatter or absorbthe acoustic signals in the attenuation region, the acoustic attenuationregion including one or more of higher density polymers than thepolymerizable materials that form a network, a scattering material,microbubbles, microballoons, a plastic material, a rubber material, oran absorptive material.
 14. The acoustic coupling medium of claim 13,wherein the scattering material includes metal or non-metal particlessized at smaller than a wavelength, or wherein the scattering materialincludes graphite, silicon carbide, aluminum oxide, silicon oxide, orsilver oxide.
 15. The acoustic coupling medium of claim 13, wherein theabsorptive material includes silicone, polyurethane, or a polymer. 16.The acoustic coupling medium of claim 1, wherein the semi-rigid materialis configurable to a flat rectangular shape, or to the tubularcylindrical shape in which the opposing ends are coupled and include agap between the opposing ends.
 17. The acoustic coupling medium of claim16, further comprising an attachment component to secure the opposingends to couple together.
 18. The acoustic coupling medium of claim 1,wherein the semi-rigid material is able to be molded to match athree-dimensional polygon shape of the receiving body.
 19. The acousticcoupling medium of claim 1, wherein the acoustic coupling medium isincluded in a system for use in tomographic ultrasound imaging, largeaperture ultrasound imaging, therapeutic ultrasound, or a combinationthereof
 20. The acoustic coupling medium of claim 1, wherein thereceiving body includes an anatomical structure of a living subjectincluding an abdomen, a thorax, a neck including a throat, an arm, aleg, a knee joint, a hip joint, an ankle joint, an elbow joint, ashoulder joint, a wrist joint, a breast, a genital, or a head includingthe cranium.